The Surgeon General's Report on Oral Health identifies dental caries as the nation's most common chronic childhood disease. Streptococcus mutans has been implicated as the one of a series of bacteria responsible for dental decay. Preventing the transmission and colonization of Streptococcus mutans from mother to child may decrease or prevent dental caries. Fluoride is the most common agent used to decrease caries and works to remineralize tooth structure. It facilitates remineralization of tooth structure and when used in sufficiently high concentrations, is an effective antimicrobial agent against smooth surface decay. Concentrations of fluoride typically found in public water supplies, dentrifrices, and professionally applied formulations are not high enough to provide antimicrobial benefit. Chlorhexidine and xylitol are two antimicrobial agents that have been used primarly outside the United States as caries preventive agents. Treatment with either chlorhexidine or xylitol, while generally proven effective against dental caries, has been controversial alone or in combination on S. mutans transmission. Therefore, we propose to assess the effects of chlorhexidine and xylitol alone and in combination on transmission of S. mutans from mother to child and on future caries development in the child. We hypothesize that a combination of xylitol and chlorhexidine will most effectively reduce the transmission of S. mutans from the mother to the child and that this reduced transmission will result in the greatest decrease in the development of dental caries in the child. Two-hundred and fifty mother-child pairs will be randomized to five treatment groups using specific inclusion and exclusion criteria. Subjects will be randomly assigned to the experimental groups (chlorhexidine mouth rinse/placebo chewing gum, xylitol chewing gum/placebo mouth rinse, and chlorhixidine mouth rinse & xylitol chewing gum) or to the control groups (placebo chewing gum/placebo mouth rinse and no treatment). The specific aims are to (i) identify the treatment that results in the largest reduction in transmission of S. mutans from mother to child, and to track the vertical transmission of S. mutans from the mother to child, and (ii) identify the treatment that results in the greatest reduction in caries development in the child and its relationship to reduced transmission of S. mutans from the mother. The success rates will be compared between the experimental and the control groups using appropriate statistical methods. The long term goal will be to use the most effective treatment as alternative intervention therapy to reduce caries, the impact of which has significant public health benefits nationwide.